The National Weather Service had anticipated heavy afternoon showers, and warned of possible flooding in some areas.

But the storm that materialized took everyone by surprise. “Back in the area where the rain had ended, a second batch of even heavier rain developed out of nowhere and parked itself right over the heart of the metro area," Gross said.

The storm ended up dumping tons of rain across the heart of Metro Detroit right at the start of rush hour.

At 7:30 pm, the Michigan State Police advised drivers to "avoid non-essential use of the Metro Detroit Freeway system…All freeways in the Metro area are currently experiencing flooding at different points.”

Others were trapped in parking lots and businesses. Emergency crews sprang into action, but many were quickly swamped by the road conditions themselves.

At the I-75 and I-696 interchange in Hazel Park, crews rescued several drivers whose vehicles were almost completely submerged after an over-taxed pumping station started gushing water onto the busy roadway.

Other dangers were not immediately obvious. Roseville Fire Chief Mike Holland warned Metro Detroiters to avoid walking across standing water on roadways.

“Manhole covers are being hidden by water and flooding can lift them out of their holes,” Holland told the Detroit News. “Pedestrians could wind up falling in.”

Sewage-flooded streets and basements have been reported all over the region. The real clean-up and damage assessment begins today.